By the use of a chemical vapour deposition technique a series of metal wires (W, Ta, Steel ) with differently shaped tips have been coated by arrays of single wall carbon nanotubes (SWNT). The field emission properties of the SWNT deposits have been measured by a home made apparatus working in medium vacuum (10-6- 10-7 mbar) and the SWNT-coated wires have been used to fabricate tiny electron sources for X-ray tubes.
To check the efficiency of the nanotube coated wires for X-ray generation has, a prototype X-ray tube has been designed and fabricated. The X-ray tube works at pressures about 10-6 mbar. The target ( Al film) is disposed on a hole in the stainless steel sheath: this configuration makes unnecessary the usual Be window and moreover allows us to use low accelerating potentials (< 6 kV).
The gas sensor based on carbon nanotubes are presently receiving considerable attention because of the outstanding
properties, such as faster response, higher sensitivity, lower operating temperature and robustness of the nanotubes in
comparison with the other types of sensing materials.
In the present research, we demonstrate detection of hydrogen at room temperature using a Quartz Crystal Nano-balance
(QCN) and as sensing material, Single-Walled Carbon Nanotubes (SWCNTs) dispersed in a polythiophene matrix. The
experimental determination of H2 in H2/N2 mixtures has been performed by using a counter frequency and observing the
frequency shifts induced in a quartz crystal resonator by H2 adsorption and consequent mass variation of the active layer
deposited on the quartz.
The high sensitivity of the realized nano-balance allows us to observe mass variations up to few nanograms /Hertz and to
detect up to 1% of H2. The good sensing performances of the nanotube-based material make unnecessary the use of any
catalyst species for H2 detection. Moreover this QCN device is able to work with good efficiency at 23 °C and 1 Atm.
The field emission properties of single-walled carbon nanotubes deposited by chemical vapour deposition on plane
substrates and on wires have been investigated. The good emitting performances of the nanotubes are promising for the
assembling of robust and efficient cold cathodes, and in particular for the use as an electron source for X-ray production.
Tiny electron sources have been fabricated by coating metal wires (W, 300 &mgr;m diameter) with nanotubes. To assess the
efficiency of such nanotube-based cathodes for generating X radiation, a prototype X-ray tube has been fabricated.
Preliminary measurements of X-ray emission obtained with such a device are presented.
For the secondary electron emission studies a series of poly- and nano-crystalline diamond films with different
characteristics (crystallinity, morphology and dopants) were produced using an innovative CVD apparatus that allows the
doping of diamond layers. Moreover additional hydrogenation processes were carried out after the first emission
experiments in order to obtain H termination at three diamond surface and enhance the electron yield. At 1 KeV a gain of
5.5 has been obtained for Ti-doped diamond layers and for diamond layers containing C-sp2 clusters.
We present here some methods for the production of organized systems formed by carbon nanotubes and suitable for
nano-beams generation and handling. In particular methodologies based on Chemical Vapour Deposition (CVD),
chemically induced assembling and alignment by dielectrophoretic processes are examined and their capacity to produce
assembling of nanostructured materials with defined architecture is discussed
The importance of nanocomposites materials such as carbon nanotubes-polymers composites for the efficient realization
of innovative solar cells based on organic as well hybrid organic-inorganic solar cells is more and more evident. We
present a study on the realization of dye sensitized solar cells (DSSC) and sublimation deposited solar cells, considering
the impact of using nanocomposite materials in the different sections composing the cells. We discuss the effect of using
poly-3,4-ethylene dioxythiophene/poly(styrene sulfonate) (PEDOT/PSS)-Carbon nanotube (CNT) blend as counterelectrode
in DSSC on the cell efficiency and fill factor, also considering DSSC structures where low cost, innovative
dyes are used. Nanocomposites can be used as solution processed or electropolimerized electrodes, where accurate
control of nanotube dispersion is obtained through specific chemical treatment of Carbon nanotubes solubility. The use
of Carbon based nanostructured material is also investigated in terms of their positive impact on the realization of
organic solar cells on flexible substrates.
We investigated the influence of the surface state of diamond layers on the characteristics of the photoemission induced by 4.7 eV photons. A series of diamond samples grown by CVD under slightly different conditions have been analysed. Polycrystalline diamond layers with nanoscale graphitic patches embedded at the grain boundaries are found to exhibit unusually high efficiency of electron photoemission. The photoemitting properties of the different samples are rationalized by considering the electron emission process located at the a-C/diamond/vacuum triple border and the quantum efficiency (Q.E). governed by the ratio of amorphous sp2-C to crystalline sp3-C. At 4.7 eV values of quantum efficiency up to 1.5 x 10-5 have been measured and the trends of the experimental Q vs J curves indicate that photoemission occurred mainly under one-photon regimes.
We have performed studies on the correlation between mechanical deformations and electrical conductance on a new interesting hybrid material, a Single Wall Carbon Nanotubes (SWCNTs)/Poly(3,4-ethylenedioxythiophene) (PEDOT) composite. Two are the synthesis techniques utilized to prepare the composite material in form of few hundreds of nm thick films: a spin coating deposition starting from an aqueous dispersion of SWCNTs and PEDOT, and an electrochemical de*position starting from a dispersion of SWCNTs and EDOT monomer. The composite conductance changes induced by a modulated periodic elongation via a coherent technique have been monitored by measuring the voltage variations of a Wheatstone bridge connected with the films. The measurements were performed on SWCNTs/PEDOT composites layered on a rigid substrate. The piezoresistivity gauge factor (GF) of the various samples was evaluated by comparing their responses to mechanical deformations to those of a commercial strain gauge, sticked on a substrate of the same kind. We found no significant piezoresistive effect in the hybrid material films deposited by means of spin coating while the effect is remarkable for the composites prepared by means of the electrochemical technique. In this case the gauge factor is found to be up to 3-4 times higher than that of the commercial strain gauge.
In the present research, purified commercially SWCNTs are used as gas sensing material in an interdigitated electrode platform for NH3, NOx and H2O detection. The SWCNT response to gas absorption is known to be dependent from different parameters and operational conditions, such as the relative orientation of the nanotubes and their organization between the electrodes, the temperature of the sensor, and moreover the voltage applied to a back gate contact. We show the sensor response for the various gas species considered and we analyze the sensor behavior with respect to the sensibility and to the detection velocity. Moreover we studied the effect on absorption/desorption gas processes by applying a gate voltage to the Si substrate beneath the interdigitated electrodes. The results indicate that the acceleration of the time response of the sensor for the detection of NH3 is proportional to the gate voltage in the range 0 V - 40 V.
We reported the design and realization of a carbon nanotube-based integrated multielectrode device. Patterned Si/SiO2/Nb/Nb2O5 multilayer was successfully realized by means of a few, common photolithographic processes with the minimum number of mask alignment steps. Such structure constitutes the patterned substrate of successive Hot Filament Chemical Vapour Deposition (HFCVD) process. Selective growth of highly oriented SWCNT arrays was obtained in the predefined locations while survival of the entire structure was achieved. Field emission measurements of such materials were carried out. Good and reproducible field emission behaviour has been observed in several realized structures.
Single Wall Carbon Nanotubes (SWCNTs) based nanotechnology appears to be promising for future nanoelectronics. The SWCNT may be either metallic or semiconducting and both metallic and semiconducting types of SWCNTs have been observed experimentally. This gives rise to intriguing possibilities to put together semiconductor-semiconductor and semiconductor-metal junctions for diodes and transistors. The potential for nanotubes in nanoelectronics devices, displays and nanosensors is enormous. However, in order to realize the potential of SWCNTs, it is critical to understand the properties of charge transport and to control phase purity, elicity and arrangement according to specific architectures. We have investigated the electrical properties of various SWCNTs samples whit different organization: bundles of SWCNTs, SWCNT fibres and different membranes and tablets obtained using SWCNTs purified and characterized.
Electrical characterizations were carried out by a 4155B Agilent Semiconductor Parameter Analyser. In order to give a mechanical stability to SWCNTs fibres and bundles we have used a nafion matrix coating, so an electrical characterization has been performed on samples with and without this layer. I-V measurements were performed in vacuum and in air using aluminium interdigitated coplanar-electrodes (width=20mm or 40mm) on glass substrates. The behaviour observed is generally supralinear with currents of the order of mA in vacuum and lower values in air with the exception of the tablet samples where the behaviour is ohmic, the currents are higher and similar values of current are detected in air and vacuum.
We have performed studies on the correlation between mechanical deformation and conductivity on a set of carbon samples constituted by 70% of single-walled carbon nanotubes. The samples, in form of slabs (6 × 5 mm, thickness: 400 mm), were obtained by compacting the nanotube material at 200 and 600 bar. The changes of conductivity have been monitored by measuring the current variations induced by a modulated periodic elongation of the slabs via a coherent technique. The mechanical deformations were produced by forces applied vertically at the center of each slab, horizontally placed on a sample holder. A piezoelectric actuator controlled by a lock-in amplifier was fixed to the sample holder. The modulation of the current induced by the mechanical deformation of the nanotube slabs is huge, and the amplitude of the modulation is almost linearly proportional to the elongation induced by the piezoelectric actuator. Such change of conductivity is more than an order of magnitude higher than the change obtained by piezoelectrical deformation of Si. The behaviour of the nanotube samples has been compared to that of a reference sample made of graphite compressed at 200 bar to form a slab with similar dimensions. In this case the change of conductivity was below the sensitivity of the lock-in amplifier, which was unable to lock to the periodicity of the mechanical deformation. We are currently addressing the problem to interpret the strong response of the nanotube slabs, which could be attributed either to a piezoresistive response of the sample or to the direct effect of the deformation on the hopping transport processes.
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